1. Field of the Invention
The invention relates to a vehicular internal gear type oil pump that has a high pressure discharge passage and a low pressure discharge passage. More particularly, the invention relates to technology for reducing the volumetric efficiency on the high pressure discharge side.
2. Description of Related Art
Japanese Patent Application Publication No. 2009-127569 (JP-A-2009-127569) describes a vehicular internal gear type oil pump that has a drive gear that has outer peripheral teeth and is provided rotatable about an axis; an annular driven gear that is provided rotatable about an offset axial center that is offset from the axis, and that is rotatably driven by the driven gear; a pump chamber that houses the driven gear and the drive gear; and a housing that has a high pressure discharge passage and a low pressure discharge passage that are open, a predetermined distance apart from each other in the circumferential direction, to a side surface of the pump chamber in order to discharge fluid (i.e., oil) from within the pump chamber. In this vehicular internal gear type oil pump, a plurality of hydraulic pressure chambers formed in the circumferential direction by mesh gaps between the inner peripheral teeth and the outer peripheral teeth move in a predetermined rotational direction with the rotation of the drive gear and the driven gear, such that the hydraulic pressure chambers become communicated with the high pressure discharge passage and the low pressure discharge passage, in order, in a process in which the volume of the hydraulic pressure chambers is reduced.
The hydraulic fluid in the low pressure discharge passage is switched between being merged with the hydraulic fluid in the high pressure discharge passage and being maintained at a low hydraulic pressure that is comparatively lower than the hydraulic pressure in the high pressure discharge passage, by a hydraulic pressure regulating device such as a regulator, for example, that is provided on the downstream side of the low pressure discharge passage. Also, if the amount of relatively high pressure hydraulic fluid that is consumed is satisfied by (i.e., does not exceed) the amount discharged from the high pressure discharge passage alone, the hydraulic fluid in the low pressure discharge passage is maintained at the low hydraulic pressure and used for lubricating or cooling, for example. Also, if the amount of relatively high pressure hydraulic fluid that is consumed is not satisfied by (i.e., exceeds) the amount discharged from the high pressure discharge passage alone, the hydraulic fluid in the low pressure discharge passage is merged with the hydraulic fluid in the high pressure discharge passage and supplied to the hydraulic pressure circuit.
Also, the vehicular internal gear type oil pump described in JP-A-2009-127569 includes a spill groove formed in a side surface of the pump chamber, so that when an entire predetermined hydraulic pressure chamber, from among the plurality of hydraulic pressure chambers, is positioned between the high pressure discharge passage and the low pressure discharge passage, the predetermined hydraulic pressure chamber is communicated with the low pressure discharge passage. Accordingly, the hydraulic fluid in the predetermined hydraulic pressure chamber, in which the pressure starts to rise when the predetermined hydraulic pressure chamber passes between the high pressure discharge passage and the low pressure discharge passage, escapes into the low pressure discharge passage through the spill groove. Therefore, it is possible to prevent the hydraulic pressure in this hydraulic pressure chamber that is closed off from suddenly rising due to the volume of this hydraulic pressure chamber being reduced, and thus it is possible to prevent the driving torque of the oil pump from increasing due to an increase in the hydraulic pressure in this hydraulic pressure chamber.
Incidentally, with the vehicular internal gear type oil pump described above, when the hydraulic pressure in the low pressure discharge passage is maintained at the low hydraulic pressure, and a predetermined hydraulic pressure chamber passes between the high pressure discharge passage and the low pressure discharge passage, the hydraulic fluid in this predetermined hydraulic pressure chamber escapes into the low pressure discharge passage through the spill groove, so the hydraulic pressure value in the predetermined hydraulic pressure chamber is reduced to the low hydraulic pressure or a pressure near there. As a result, fluid flows between the inner peripheral teeth and the outer peripheral teeth (i.e., the tip clearance) and into the predetermined hydraulic pressure chamber from the high pressure discharge passage, i.e., an oil leak occurs, due to a difference between the hydraulic pressure value in the predetermined hydraulic pressure chamber and the hydraulic pressure value in a hydraulic pressure chamber that is adjacent to this predetermined hydraulic pressure chamber and that is communicated with the high pressure discharge passage. As a result, the volumetric efficiency of the high pressure discharge side may decrease.